Fluid actuated press

ABSTRACT

The press includes a base structure carrying a lower press platen and a head carrying an upper press platen, the head being movable on guides toward and away from the base. A fluid-actuated cylinder is carried on the movable head and is adapted to rotate a centrally located torque tube. The torque tube is connected by load transfer bars to a pair of bell cranks at each of the opposite ends of the press. The bell cranks are pivotally carried by the head. Connector rods pivotally connect between the bell cranks and the base. When the cylinder is selectively extended and retracted, the transfer bars rotate the bell cranks to respectively lower and raise the upper press platen, the bell cranks providing a mechanical advantage. With the foregoing press configuration torsional deflection, elongation of the various parts and side thrust are substantially minimized.

United States Patent [191 J ureit et al.

[ FLUID ACTUATED PRESS [75] Inventors: John Calvin Jureit, Coral Gables;

Larry Brodsky, Miami, both of Fla. [73] Assignee: Automated Building Components,

Inc., Miami, Fla.

[22] Filed: Aug. 14, 1972 [21] Appl. No.: 280,256

[52] US. Cl 100/269 R, 100/52, 100/222, 100/258 A, 100/271 [51] Int. Cl. B30b l/32 [58] Field of Search IOO/DIG. 13, 52, 270, 271, 100/258 R, 258 A, 222, 269 R; 227/152 [56] References Cited UNITED STATES PATENTS 3,605,608 9/1971 Dagley 100/271 2,224,968 12/1940 Klocke 100/271 X 2,580,078 12/1951 Denison 100/269 X 3,443,513 5/1969 Jureit et a1 100/222 X 1,062,465 5/1913 Hill"... 100/271 X 2,105,053 l/l938 Patrick 100/271 2,204,413 6/1940 Hubbert 100/271 [451 Apr. 23, 1974 2,356,790 8/1944 Horne 100/271 X Primary Examiner-Billy J. Wilhite Attorney, Agent, or FirmLeBlanc & Shur 57] ABSTRACT The press includes a base structure carrying a lower press platen and a head carrying an upper press platen, the head being movable on guides toward and away from the base. A fluid-actuated cylinder is carried on the movable head and is adapted to rotate a centrally located torque tube. The torque tube is connected by load transfer bars to a pair of bell cranks at each of the opposite ends of the press. The bell cranks are pivotally carried by the head. Connector rods pivotally connect between the bell cranks and the base. When the cylinder. is selectively extended and retracted, the transfer bars rotate the bell cranks to respectively lower and raise the upper press platen, the bell cranks providing a mechanical advantage. With the foregoing press configuration torsional deflection, elongation of the various parts and side thrust are substantially minimized.

13 Claims, 5 Drawing Figures BBOESBEM 'MEMTED APR 2 3 m SHEET 2 OF 3 VATFIHEI] APR 2 3 i974 SHEET 3 OF 3 FLUID ACTUATED PRESS The present invention relates to a novel and improved press and particularly relates to a press of the type useful for embedding connector plates into the joints of wooden trusses, panels and the like.

The building construction indsutry has recently made tremendous strides forward with the advent of prefabricated wooden trusses, panels, and the like. Such trusses comprise wooden framing members, in most cases, fastened together at their joints by connector plates, for example, plates of the type disclosed in U.S. Pat. No. 2,877,520 of common assignee herewith. A number of methods for applying the connector plates to the framing members at each joint, such as handnailing, utilizing individually operated presses, etc., have variously proven time consuming, laborious, expensive and not susceptible to large-scale automated truss or panel fabrication techniques.

Truss fabrication techniques have, however, advanced to the state where power operated presses for embedding the connector plates into the joints of the wooden framemembers are now commonly utilized. One such truss fabrication technique provides for the prepositioning of the frame members on a jig table in the pattern of the truss or panel with the connector plates spotted on opposite sides of the joints of such members. Thereafter, the connector plates are pressed into the joints to fasten the frame members together and form the completed truss, panel or the like. Presses capable of providing the foregoing action are disclosed in U.S. Pat. Nos. 3,079,607 and 3,195,449 of common assignee herewith.

In U.S. Pat. Application Ser. No. 867,730 filed Oct. 20, 1969, now U.S. Pat. No. 3,603,244 of common assignee herewith, there is disclosed a toggle-actuated press mounted for movement along a track and a control system for periodically stopping the press in a pressing position with the press platen located over the connector plates at the joints of the wooden members. The press of that application is disclosed more fully in U.S. Pat. No. 3,520,252 issued July I4, 1970, also of common assignee herewith. In U.S. Pat. application Ser. No. 190,724 filed Oct. 20, 1971, now U.S. Pat. No. 3,750,562 which issued Aug. 7, I973, of common assignee herewith, there is disclosed a fluid-actuated press constituting an improvement in the press disclosed in U.S. Pat. No. 3,520,252 and particularly useful for pressing asymmetrical loadings. Asymmetrical loadings on the press are caused by the differences in location of the joints of the various types and sizes of trusses relative to the press platen. The press disclosed in latter application Ser. No. 190,724 is particularly useful where asymmetrical loadings are anticipated.

The capacities of the foregoing presses are, however, insufficient for handling pressing operations throughout the full range of loadings anticipated in the construction of the various types of trusses, panels and the like. For example, the foregoing described presses do not have the capacity to embed connector plates into the joints of large, heavy trusses, for example pole-barn trusses. Pole-barn type trusses are extremely heavy trusses which have top and bottom chords typically formed of 2 X 12 and 2 X framing members. Due to the various wood densities, tooth sizes and particularly the number of teeth per joint, (which in turn depends on the size of the members of the truss) these large heavy trusses often require tons or more force to embed the teeth of the connector plates at just one joint. The foregoing described presses simply do not have the capacity to apply this magnitude of pressing force. The problem, however, is not one of merely increasing the size of the press to increase its capacity since there are practical, economical, and mechanical limitations on scaling up existing presses to meet the required capacity. for example, there are limitations in use of materials at these high loadings, for example on the order of a tons which are not present under lower loadings. Also, deflection of press members due to elongation or twisting under loading as well as the developed side thrust become problems. Further, economic considerations indicate use of a single power cyl inder rather than a pair of pairs of cylinders for actuating the press head as in prior presses.

The present invention provides a fluid actuated press which minimizes and/or eliminates the foregoing and other problems associated with prior presses of this type and provides a novel and improved fluid actuated press having various advantages in construction, mode of operation and result as compared with the foregoing described presses. The press hereof is particularly adapted for embedding nail plates into the joints of wooden members forming trusses, panels and the like and is particularly characterized by a capacity to embed connector plates into the joints of trusses, panels and the like throughout the full range of anticipated sizes and types of trusses and their associated joint requirements.

To accomplish this, the present invention provides a lower support structure or base carrying a lower press platen and a floating head carrying an upper press platen. The head is slidable along guide bars connected to the base for reciprocating movement of the upper platen toward and awayfrom the lower platen. A single fluid-actuated cylinder is carried by the floating head and has its piston connected with a centrally disposed transversely extending torsion tube for rotating the latter. The torsion tube, in turn, carries arms at opposite ends which connect with pairs of transfer bars. Each pair of transfer bars extends to opposite ends of the press where they are connected to bell cranks pivotally carried by the floating head. Pivotally connected rods connect between the bell cranks and the base of the press adjacent each corner thereof.

In operation, actuation of the cylinder to extend its piston pivots the bell cranks through the torsion tube, and transfer bars to move the upper press platen toward the lower press platen. In moving the upper press platen, the vertically extending connecting rods pivot through a very slight arc and thus develop onlynominal side thrust. The bell cranks provide a mechanical advantage whereby a pressing force approximately 2 n times the capaciy of the single cylinder is provided at any point along the press or is distributed over the area of the press platens.

The foregoing design minimizes torsional deflection. That is, torsional loads are transferred only through the central torsion tube and which tube has only a nominal length. No torsion transfer is effected between the bell cranks at the end of the press or at any other location along the press. Moreover, located between the poweractuated cylinder and the bell cranks which provide the mechanical advantage, the sum of any torsional deflections and/or elongations of the transfer bars is mini- 3 mized by a factor of the mechanical advantage. For example, if a maximum deflection at the top of the bell crank due to torsional deflection and elongation of transfer bars is 0.1 inch, this is reflected in press deflection of about 0.04 inches due to the reduced effect of such deflections and elongations by the inter-position of the bell cranks.

Accordingly, it is a primary object of the present invention to provide a novel and improved press for embedding connector plates into the joints of prepositioned wooden members forming trusses, panels, and the like.

It is another object of the present invention to provide a novel and improved press having a capacity to embed connector plates into the joints of trusses, panels and the like ranging in size from the smallest to the largest. v

It is still another object of the present invention to provide a novel and improved press which is constructed to minimize press deflection due to elongation or twisting of the operating members of the press.

It is a further object of the present invention to provide a novel and improved press which develops only nominal side thrust throughout its full capacity.

It is a still further object of the present invention to provide a novel and improved press which is simple in construction, economical to manufacture, and has 21 capacity for applying maximum loadings at any point along the press or an equal distribution of the loading throughout the area of the press.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings wherein:

FIG. 1 is a side elevational view of a press constructed in accordance with the present invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is an end elevational view of the trated in FIG. 1;

FIG. 4 is a cross-sectional view thereof taken generally about on line 4-4 in FIG. 1; and

FIG. 5 is a schematic illustration of the fluid system for'usein operating the press hereof.

Referring now to the drawings, particularly to FIG. 1, there'is illustrated a press, generally indicated 10, comprised of a base structure 12 and an upper head 14 movable toward and away from base structure 12. The upper edge of base structure 12 mounts a lower press platen 16 while the lower edge of the movable head 14 carries an upper press platen 18. The press is supported by a plurality of legs 20 secured to the underside of base structure 12. lt-will be appreciated that the press hereof may be utilized with the truss fabricating system described and illustrated in U.S. Pat. No. 3,602,237 issued Aug. 31, 1971, of common assignee herewith, the disclosure of which application is incorporated herein by reference thereto as though fully set'forth herein. It will be appreciated that the press hereof can be substituted for the press disclosed in that truss fabricating system and, to this end, the chain drive for the jig table disclosed in that system is adapted to pass through the present press. Particularly, the lower press platen 16 is interrupted at 22 to provide a slot for receiving the endless chain which drives the jig table through the press. Also, a tube 24 extends through the base structure 12 and carries the lower portion of the endless chain through the press in' the opposite direction.

press illus- Referring to FIG. 4, the upper and lower heads 14 and 12, respectively, each comprise box-like structures including --a plurality of transversely spaced webs 24. The webs of head 14 are joined along their lower edges to the upper press platen 18 while the webs 24 of the lower head 12 are joined along their upper edges by the lower press platen 16. The top of head 14 is closed by a plate 26 secured along the upper edges of webs 24 and the bottom of head 12 is closed by a plate 28 secured along the lower edges of webs 24. An intermediate web 24 and a side web plate 30 of the lower head 12 form a chamber 32 which defines a reservoir for the fluid actuated press hereof as hereinafter set forth. As best illustrated in FIG. 1, inlet and outlet connections 34 and 36 to chamber 32 are provided through the side plate 30 for connection with the fluid system to be described.

The lower head 12 is closed at opposite ends by end plates 38. Each end plate 38 mounts a pair of vertically aligned sockets 39 at opposite sides of the plate and which aligned sockets receive guidebars 40. Opposite ends of the upper head I4 are closed by end plates 42 each of which carries a pair of sockets 44 in registry with the sockets 39. Each socket 44 slidably receives the upper end of a guidebar 40. The guidebars 40 thus serve to maintain the upper head 14 in accurate vertical registry with the base 12 throughout the full range of movement of head 14 relative to base 12.

For operating the press, the upper press head 14 carries a cylinder generally indicated 50, a torque tube assembly generally indicated 52, a transfer assembly generally indicated at 54 and a transfer tube assembly generally indicated 56. Particularly, a cylinder mounting bracket 58 is secured to the upper plate 26 of head 14 and pivotally mounts one end of the cylinder 50 by a clevis'and pin joint indicated 60. The mounting bracket lies to one side of the transverse centerline of the press and the piston rod 62 of cylinder 50 is pivotally connected between a pair of plates 64 at their distal ends and which plates form a crank arm and part of the torque tube assembly 52. The opposite ends of the plates 64 are secured as by welding to a troque tube 66. Torque tube 66 is mounted for rotation about a primary shaft 68 secured at opposite ends to a pair of upright supports 70 located along opposite sides of the press. Adjacent opposite ends of torque tube 66 there is provided a lever 71 comprised of a pair of torque transfer plates 72 suitably secured as by welding to tube 66. It will be appreciated that actuation of cylinder 50 operates through crank arm 64 to rotate torque tube 56 in one direction upon extension of piston 62 and in the opposite direction of piston 62. Opposite ends of levers 71 are connected with respective left and right hand transfer assemblies generally indicated 74 and 76. Each transfer assembly includes a pair of transfer bars 78 with each bar 78 comprised of a tube 79 having stub shafts 80 and 82 secured at opposite ends. The left and right hand transfer assemblies 74 and 76 are identical one with the other with the exception that the inner ends of the transfer bars 78 connect at opposite ends of the levers 71. Accordingly, the stub shafts 82 of the inner end of the left hand transfer bars 78 are pivotally connected to like ends of levers 71 on one side of torque tube 66 and between spaced plates 72 by pins 84 while the ends of shafts 82 of the right hand transfer assembly 76 are pivotally connected to the like ends of levers 71 on the other side of torque tube 66 and between plates 72 by pins 86. The stub shafts at the opposite ends of the transfer assemblies 54 are pivotally connected with respective transfer tube assemblies 56.

Each transfer tube assembly 56 includes a tube encompassing a primary shaft 92 rigidly secured at opposite ends to a pair of mounting plates 93 secured on opposite sides of head 14 at opposite ends of the press. Each tube 90 mounts a bell crank 94 adjacent its opposite ends for rotation with the tube 90. Each bell crank 94 comprises one pair of spaced plates 95 which project upwardly above head 14. Each pair of plates 95 receives the end of stub shaft 80 therebetween with shafts 80 being pinned to bell cranks 94 at 98. The opposite legs of the bell cranks are pinned as at 99 to the upper ends of connecting rods 100. Each connecting rod 100 is pivotally connected at its lower end to the base 12 by a clevis and pin connection 102. Accordingly, it will be appreciated that movement of the bell cranks, for example, the left hand bell cranks illustrated in FIG. 1, in a clockwise direction, (with corresponding movement of the right hand bell cranks in a counterclockwise direction), will cause head 14 and hence platen 18 to move toward the lower platen 16. Conversely, pivotal movement of the left hand bell cranks about primary shaft 92 in a counterclockwise direction as illustrated in FIG. 1 (with corresponding movement of the right hand bell cranks in a clockwise direction) causes the upper head 14 to move away from base 12.

Turning now to FIG. 5, there is illustrated a fluid circuit for operating the press hereof. Particularly, the fluid circuit includes a double pump unit generally indicated driven by an electric motor 112. Pump of double pumping unit 110 is adapted to pump fluid from reservoir 114 through a conduit 116, a 4-way, 3- position solenoid actuated spring return directional control valve 122 and into a conduit 124 which in turn communicates with a similar value 126. Pump 121 of pump unit 110 is adapted to pump fluid via a conduit 118 to conduit 124 whereby valve 122 is bypassed. Conduits 128 and 130 connect valve 126 with opposite sides of cylinder 50. A return conduit 132 communicates between valve 126 and a reservoir 114. A conduit 134 connects between a conduit 128 and a pressure switch 136. Through suitable electrical circuitry, not shown, switch 136 is adapted to actuate solenoid 138R to shift valve 126 to the right as seen in FIG. 5 in response to predetermined pressure in the fluid system for purposes hereinafter set forth. An unloading valve 140 lies in communication with conduit 118 and is set at a predetermined pressure to unload pump 121 into reservoir 114. A check valve 142 is downstream of unloading valve 140 in conduit 141 whereby reverse flow from conduit 124 through conduit 118 is precluded.

Conduits and 152 connect between valve 122 and a flow regulator 154 through a cushion valve 15. Regulator 154 communicates with the hydraulic motor 158 which is adapted to drive the chain for advancing or retracting the jig table through the press, the chain and jig table not been shown herein. A 4-way control switch, also not shown, is provided for actuating the solenoids 138L and 138R associated with valve 126 and 160A and 160R associated with valve 122.

When the fluid system is idling and with valves 122 and 126 spring centered, flow from the double pump unit 110 flows through conduits 116, 118, 124 and 132 into reservoir 114. When the press is to be actuated, the control switch is actuated to energize solenoid 1381.. to shift valve 126 to the left as seen in FIG. 5 whereby flow from conduit 124 passes through valve 126 and conduit 128 into cylinder 50 to extend its piston. The flow supplies fluid at high volume and low pressure to the cylinder 50. As will be recalled, extension of the piston results in movement of the upper press platen downwardly toward the lower press platen. When a predetermined system pressure is obtained, i.e., about a 1000 psi, unloading valve 140 is actuated and the fluid from conduit 118 is dumped to reservoir 114. Fluid from pump 120, however, continues to flow via conduits 116 and 124 into cylinder 50 whereby fluid is supplied at low volume and high pressure. When a predetermined pressure is obtained and after the connector plates are fully embedded into the joints of the truss, panel or the like, pressure switch 136 is actuated and energizes solenoid 138 whereupon valve 126 is shifted to the right as seen in FIG. 5. Fluid is thus supplied from motor 120 via conduits 116, 124 and 130 to the opposite side of the piston to retract it and thereby raise the upper press platen relative to the lower press platen. It will be appreciated that the fluid exhausts through conduit 128 into conduit 132 for return to reservoir 114.

The foregoing described system may be described in terms of a high/low system. That is, high volume at low pressure is initially provided the system upon initial movement of the upper press platen toward the lower press platen. At a predetermined pressure, fluid is supplied at low volume high pressure to achieve maximum pressing force upon closing the press platens.

For moving the jig table through the press, the operator shifts the control switch to energize solenoid 160A to shift valve 122 whereby fluid under pressure is provided motor 158 via conduit 116 and 152 for actuating the chain drive and advancing the jig table through the press. By shifting the control switch to another position, solenoid 160R is energized to shift valve 122 thereby supplying fluid for operating motor 158 in reverse and hence reversing the travel of the jig table through the press.

lna preferred embodiment hereof, the output of cylinder 50 is 76,000 lbs. The bell cranks are formed and connected to provide a 2.6 to l mechanical advantage whereby upon actuation of the cylinder, a pressing force of substantially 200,000 lbs. is developed. With the foregoing described press and fluid system therefor, the press is capable of cycling at full tonnage in three seconds and at half tonnage capacity in 2.5 seconds. in order to minimize development of side thrust, the connector rods 100 are located in a ture vertical position when the gap between the press platens is about 2.5 inches. This gap is determined by a consideration of the thicknesses of the jig table and lumber and making allowance for lumber compression during nail seating. Thus, the connector rods 100 are substantially on a true vertical position when maximum pressing force is applied.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within structure whereby the platen carried by said head is movable toward and away from the platen carried by said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platens, said coupling means including a connecting rod at each end of said press, each of said connecting rods being pivotally coupled at one end to said base structure and at its other end to the bell crank at the like end of said press.

2. A press according to claim 1 wherein said connecting rods extend vertically of said press for a predetermined spacing of said press platens one from the other, said rods being movable to respective over-center positions in response to opening or closing movement of the press from said predetermined spacing of said platens.

3. A press according to claim 1 wherein said base structure defines a chamber for containing fluid for operating said cylinder, and means connecting opposite ends of said cylinder with said chamber.

4. A press according to claim 1 including a slot formed in the lower press platen, and an opening in vertical registry below said slot through said base structure for receiving a drive mechanism.

5. A press according to claim 1 wherein the platens carried by said base structure and said head comprise lower and upper platens, respectively.

6. A press for use in fabricating wooden panels, trusses or the like comprising: a base structure including a press platen, a head including a press platen in opposition to said first mentioned press platen, means connecting said head and said base structure for movement of said head toward and away from said base structure whereby the platen carried by said head is movable toward and away from the platen carried by a said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platens, said-coupling means including a lever carried by said head for pivotal movement about an axis intermediate its ends, means connecting said lever and said cylinder for rotary movement of said lever in response to actuation of said cylinder, a pair of linearly extending transfer bars, one of said transfer bars being pivotally connected to one end of said lever and at its opposite end to the bell crank at one end of said press, the other of said transfer bars being pivotally connected at one end to the opposite end of said lever and at its opposite end to the bell crank at the other end of said press.

7. A press according to claim 6 wherein said coupling means includes a connecting rod at each end of said press, each of said connecting rods being pivotally connected at one. end to the bell crank at the like end of said press and at its opposite end to said base structure.

8. A press according to claim 7 including a shaft carried by said head, said connecting means between said lever and said cylinder including a torque tube carried by said shaft and a crank arm carried by said torque tube, said cylinder being pivotally carried by said head and having its piston rod pivotally connected to said crank arm for rotating said tube and lever.

9. A press for use in fabricating wooden panels, trusses or the like comprising: a base structure including a press platen, a head including a press platen in opposition to said first mentioned press platen, means connecting said head and said base structure for movement of said head toward and away from said base structure whereby the platen carried by said head is movable toward and away from the platen carried by said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platen, said coupling means including a pair of bell cranks pivotally carried by said head at each of the opposite ends of said press and coupled to said cylinder and said base structure, a pair of levers carried by said head adjacent a central portion thereof and adjacent opposite sides of said press for pivotal movement about a common axis intermedia the ends of said levers, means connecting said levers and said cylinder for rotating said levers in response to actuation of said cylinder, first and second pairs of transfer bars, said first pair of transfer bars being pivotally connected at like ends to respective like ends of said levers and at their opposite ends to respective bell cranks'at one end of said press, said second pair of transfer bars being pivotally connected at like ends to the respective opposite ends of said levers and at their opposite ends to respective bell cranks at the other end of said press.

10. A press according to claim 9 including a shaft carried by said head, said connecting means between said levers and said cylinder including a torque tube carried by said shaft and a crank arm carried by said torque tube, said levers being carried by said torque tube on opposite sides of said crank arm, said cylinder being pivotally carried by said head and having a piston rod pivotally connected to an end of said crank arm for rotating said torque tube and levers.

11. A press according to claim 10 wherein said coupling means includes a pair of connecting rods at each end of said press, the connecting rods at one end of said press being pivotally connected at like ends to the respective bell cranks at said one press end and at their opposite ends to said base structure, the connecting rods at the opposite end of said press being pivotally movement of the press from said predetermined spacing of said platens.

13. A pressaccording to claim 10 including a shaft carried at opposite ends of said press, and means coupling between the bell cranks at like ends of said press including a tube pivotally carried by said shaft and mounting said bell cranks.

EXIT ID SZXTES PJCIZXT CFFICE CERTIFICATE OF CQRRECTIQN Patent 220. r 3 a Dated April 23 1974 o lnventofls) John Calvin Jureit and Larry Brodsky It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 2, line 16, "pair of pairs" should read --pair or hairs-w In Column 5, line 39', "value" should read ---valve--; line 57, 'valve 15" should read --valve l56-.

In Column 6, line 53, "ture" should read --,true--.

In Column 8, line 40-41, "intermedia" should read --i.ntermediate--.

Signed and sealed this 1st day of October 1974.

(SEAL) I Q Attest:

McC'OY M. GIBSON-JR. c. MARSHALL DANN Attesting Officer Comnfissioner of Patents 

1. A press for use in fabricating wooden panels, trusses or the like comprising: a base structure including a press platen, a head including a press platen in opposition to said first mentioned press platen, means connecting said head and said base structure for movement of said head toward and away from said base structure whereby the platen carried by said head is movable toward and away from the platen carried by said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platens, said coupling means including a connecting rod at each end of said press, each of said conneCting rods being pivotally coupled at one end to said base structure and at its other end to the bell crank at the like end of said press.
 2. A press according to claim 1 wherein said connecting rods extend vertically of said press for a predetermined spacing of said press platens one from the other, said rods being movable to respective over-center positions in response to opening or closing movement of the press from said predetermined spacing of said platens.
 3. A press according to claim 1 wherein said base structure defines a chamber for containing fluid for operating said cylinder, and means connecting opposite ends of said cylinder with said chamber.
 4. A press according to claim 1 including a slot formed in the lower press platen, and an opening in vertical registry below said slot through said base structure for receiving a drive mechanism.
 5. A press according to claim 1 wherein the platens carried by said base structure and said head comprise lower and upper platens, respectively.
 6. A press for use in fabricating wooden panels, trusses or the like comprising: a base structure including a press platen, a head including a press platen in opposition to said first mentioned press platen, means connecting said head and said base structure for movement of said head toward and away from said base structure whereby the platen carried by said head is movable toward and away from the platen carried by said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platens, said coupling means including a lever carried by said head for pivotal movement about an axis intermediate its ends, means connecting said lever and said cylinder for rotary movement of said lever in response to actuation of said cylinder, a pair of linearly extending transfer bars, one of said transfer bars being pivotally connected to one end of said lever and at its opposite end to the bell crank at one end of said press, the other of said transfer bars being pivotally connected at one end to the opposite end of said lever and at its opposite end to the bell crank at the other end of said press.
 7. A press according to claim 6 wherein said coupling means includes a connecting rod at each end of said press, each of said connecting rods being pivotally connected at one end to the bell crank at the like end of said press and at its opposite end to said base structure.
 8. A press according to claim 7 including a shaft carried by said head, said connecting means between said lever and said cylinder including a torque tube carried by said shaft and a crank arm carried by said torque tube, said cylinder being pivotally carried by said head and having its piston rod pivotally connected to said crank arm for rotating said tube and lever.
 9. A press for use in fabricating wooden panels, trusses or the like comprising: a base structure including a press platen, a head including a press platen in opposition to said first mentioned press platen, means connecting said head and said base structure for movement of said head toward and away from said base structure whereby the platen carried by said head is movable toward and away from the platen carried by said base structure, a fluid actuated cylinder carried by said head, and means coupled to said cylinder and between said base structure and said head at opposite ends of said press for moving said head toward and away from said base structure, said coupling means including a bell crank pivotally carried by said head at opposite ends of the press and coupled to said cylinder and said base structure whereby a mechanical advantage is obtained at the press platen, saId coupling means including a pair of bell cranks pivotally carried by said head at each of the opposite ends of said press and coupled to said cylinder and said base structure, a pair of levers carried by said head adjacent a central portion thereof and adjacent opposite sides of said press for pivotal movement about a common axis intermedia the ends of said levers, means connecting said levers and said cylinder for rotating said levers in response to actuation of said cylinder, first and second pairs of transfer bars, said first pair of transfer bars being pivotally connected at like ends to respective like ends of said levers and at their opposite ends to respective bell cranks at one end of said press, said second pair of transfer bars being pivotally connected at like ends to the respective opposite ends of said levers and at their opposite ends to respective bell cranks at the other end of said press.
 10. A press according to claim 9 including a shaft carried by said head, said connecting means between said levers and said cylinder including a torque tube carried by said shaft and a crank arm carried by said torque tube, said levers being carried by said torque tube on opposite sides of said crank arm, said cylinder being pivotally carried by said head and having a piston rod pivotally connected to an end of said crank arm for rotating said torque tube and levers.
 11. A press according to claim 10 wherein said coupling means includes a pair of connecting rods at each end of said press, the connecting rods at one end of said press being pivotally connected at like ends to the respective bell cranks at said one press end and at their opposite ends to said base structure, the connecting rods at the opposite end of said press being pivotally connected at like ends to the respective bell cranks at the other end of said press and at their opposite ends to said base structure.
 12. A press according to claim 11 wherein said connecting rods extend vertically of said press for a predetermined spacing of said press platen one from the other, said rods being movable to respective over-center positions in response to opening or closing movement of the press from said predetermined spacing of said platens.
 13. A press according to claim 10 including a shaft carried at opposite ends of said press, and means coupling between the bell cranks at like ends of said press including a tube pivotally carried by said shaft and mounting said bell cranks. 